Adaptive (RLC) segmentation

ABSTRACT

A method and nodes for providing adaptive segmentation in a higher protocol layer interacting with a lower protocol layer. An adaptable segmentation limit, defining a threshold of a largest Protocol Data Unit (PDU) that is to be submitted to a lower protocol layer, is deployed at a higher protocol layer interacting with the lower protocol layer. For each Service Data Unit (SDU) arriving at the higher protocol layer, it is determined if the respective SDU can fit into the segmentation limit or not. Each SDU that do not fit into the segmentation limit is segmented into PDUs which are smaller than or equal to the segmentation limit, while no segmentation is performed on SDUs that fit into the segmentation limit.

This application is a continuation of U.S. patent application Ser. No.12/278,649, filed Aug. 7, 2008, which is a national stage application ofPCT/SE2007/050061, filed Feb. 5, 2007, and claims benefit of U.S.Provisional Application 60/743,241, filed Feb. 7, 2006, the disclosuresof each of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates generally to the field of segmentation andconcatenation of Service Data Units (SDUs) into Protocol Data Units(PDUs) in a higher protocol layer, and more particularly of reducing theoverhead due to segmentation and/or concatenation.

BACKGROUND

In the Universal Mobile Telecommunications System (UMTS) a generalprotocol reference model containing a layered protocol stack is used forproviding reliable communication of user data and signalling between thenodes of the network. UMTS also employs the concept of control-plane anduser-plane, where the control-plane is a set of protocols usedexclusively for control signalling purposes, while the user-plane isused exclusively for user data transfer.

A user-plane protocol stack in UTRAN according to the prior art isillustrated in FIG. 1. The figure illustrates the protocol stack of aUser Equipment (UE) 100 communicating with a Serving Radio networkController (SRNC) 110 and an intermediate Node B 120. The Physical layer(PHY) 101,121 offers services to the Medium Access (MAC) layers viatransport channels, while the MAC layers (MAC_e/hs/d) 102,103,111,122,in turn, offers services to the Radio Link Control (RLC) layer 104,112by means of logical channels. MAC-d handles dedicated channels, whichmay be mapped to common transport channels, wherein MAC-d passes data toMAC-hs or MAC-e. MAC-hs denotes the downlink MAC entity and is used forserving the High Speed Downlink Shared Channel (HS-DSCH), introduced inRelease 5 of the 3GPP specification, while MAC-e denotes a MAC entityrelated to the new uplink channel, Enhanced Dedicated Channel (E-DCH),introduced in Release 6.

In the user-plane, which is illustrated by the figure, the RLC layeroffers services to the Packet Data Convergence Protocol (PDCP) 105,113.A control-plane may be illustrated by simply changing the PDCP layer toa Radio Resource Control (RRC) layer.

A Service Data Unit (SDU) can be conceptualized as a data unit receivedfrom, or submitted to, a higher protocol layer, e.g. RLC. A ProtocolData Unit (PDU) is a unit which is submitted to, or received from, aprotocol layer logically located beneath the protocol from which the SDUis received. The PDU comprises a mandatory header and, optionally also aLength Indicator (LI), which indicates the last octet of eachhigher-layer SDU, ending within the PDU. The PDU also comprises a datafield, containing one or more segments from one or more higher-layerPDUs.

The RLC protocol provides radio bearers for user data transfer andsignalling radio bearers for control signalling and includesfunctionality such as RLC segmentation, re-assembly, and potentiallyalso concatenation of RLC SDUs into RLC PDUs. At the transmitting end,segmentation and/or concatenation is used in order to match currentlyused Transport Formats (TF), i.e. predetermined PDU sizes. In thereceiving end the segments belonging to one higher-layer PDU arere-assembled before they are delivered to the higher-layer. An RLC SDUis typically an IP Packet or a signalling message, while an RLC PDUtypically is a MAC_d SDU. If a higher-layer PDU segment does notcompletely fill the payload field of the RLC PDU, the first segment inthe next higher-layer PDU may be put in the RLC PDU in concatenationwith the last segments of the previous higher-layer PDU.

The RLC protocol includes the three different modes Transparent Mode(TM), Unacknowledged Mode (UM) and Acknowledged Mode (AM). In AM, theRLC deploys re-transmission to guarantee lossless delivery of all RLCPDUs, while no re-transmission, and, hence, no guarantee of datadelivery is deployed in UM. In TM, no protocol overhead is added by theRLC layer. The present invention is applicable to the UM and AM modes.

Both UM and AM of RLC uses segmentation and optionally concatenation onthe transmitter side, while re-assembly is used on the receiver side.

In the current UTRAN architecture, the RLC protocol is terminated in theServing Radio Network Controller (SRNC) and in the User Equipment (UE),respectively. The present invention does, however, not preclude adifferent architecture, where the terminating point of the protocoldeploying segmentation, re-assembly and concatenation is placedelsewhere, e.g. in the base station (node B). The RLC PDUs are submittedto, and received from, the Medium Access Control (MAC) protocol, whichrealizes the transport channels over the UMTS air-interface, the Uuinterface.

In the existing UTRAN protocol stack, the RLC PDU size for a given radiobearer can only take a discrete number of different sizes, which areconfigurable by upper layers of the protocol stack. For RLC AM, the RLCPDU size can only take a single value. The most commonly used RLC PDUsize for user-plane transmissions is 320 bits of payload and a 16 bitsRLC header. It can be configured and re-configured by higher-layers, andbearers carrying signalling typically deploy a PDU size, carrying 128bits of payload.

For RLC UM, there is a possibility to configure several RLC PCU sizes.The header fields in MAC-hs and MAC-e, however, restrict the de-factonumbers of different sizes that can be used. For example, it iscurrently possible to use maximally eight different MAC-d PDU sizes overHS-DSCH, where a MAC-d PDU is an RLC PDU and an optional MAC-d header.

The fact that the RLC PDU size can only take one single size, or adiscrete set of sizes, means that RLC SDUs typically need to besegmented and/or concatenated into an appropriate number of RLC PDUs.One drawback with such a limitation can be extensive protocol overheadand padding. Padding occurs if concatenation cannot be used, i.e. theremaining payload to be segmented into an RLC PDU does not fill theavailable space of the most suitable RLC PDU size. Such a situation canbe illustrated with the two following examples.

In a first example we consider the transmission of one 1500 octet IPpacket. It is assumed that an RLC PDU size of 320 bits, i.e. 40 octets,is used for segmentation. This implies that the IP packet is segmentedinto 38 RLC PDUs, having the capacity of delivering 1520 octets.

In this case, the RLC header overhead equals 38*2 octets and a one octetlength indicator, inserted in the last RLC PDU, which makes a total of77 octets, while padding, which is used to fill up the last RLC PDU,equals 19 octets. This means that for the transmission of 1500 octets, atotal RLC overhead of 96 octets will be necessary.

In a second example, the transmission of one compressed TransportCommunication Protocol Acknowledgement (TCP ACK) is considered. A TCPACK is typically 40 bytes long. In this example it is assumed that a TCPACK is compressed down to four octets by a conventional headercompression protocol. The RLC protocol adds a two octet fixed header anda one octet length indicator and adds padding up to the full RLC PDUsize. With the typical RLC PDU size of 320 bits, this implies a 38 octetheader overhead and padding for transmission of just four octets ofpayload.

The first example clearly illustrates the deficiency of using fixed RLCPDUs when segmenting and/or concatenating large RLC SDUs, while thesecond example shows the inefficiency which may occur when segmentingand/or concatenating small RLC SDUs.

To overcome the problems mentioned above, an RLC protocol that is ableto use any RLC PDU size has been proposed in R2-052508 “User planeprotocol enhancements”, presented at TSG-RAN WG2 Meeting#48bis,Cannes,France, 10-14 Oct. 2005. Such a flexible RLC solution mayallow arbitrary RLC PDU sizes, such that the RLC PDU equals the size ofthe RLC SDU and the necessary RLC header, and may also provide a minimallevel of RLC overhead. In addition, such a solution may remove the needfor padding. In the first example, mentioned above, the requiredoverhead with the solution proposed in R2-052508 “User plane protocolenhancements”, would be 2 octets, as opposed to 96 octets. In bothexamples, the padding would be zero octets, as opposed to 19 and 38 inthe first and second example, respectively.

Still, a problem of handling large RLC SDUs, i.e. large IP packets orlong signalling messages may occur also when using the solution referredto in R2-052508, especially when transmission coverage and RLC AMre-transmission efficiency is considered.

This deficiency can be illustrated in a first scenario, wherein a largeSDU PDU of 1500 octets is forwarded to the MAC protocol as a single RLCPDU, without deploying any segmentation. The transmission of the RLC PDUin a single transport block in MAC-hs or in MAC-e may lead to coverageproblems, i.e. a sufficiently large transport block may not be supportedin the whole cell, which may result in a failure to deliver the largeRLC PDU. In other words, if the link quality between a user equipmentand a radio base-station is bad, the MAC protocol may fail to deliversuch a large block as a single transmission unit. Trying to solve thescenario described above by adapting the transmission blocks size to thelink-quality by introducing segmentation and concatenation into MAC, maynot be adequate, since such a solution may result in a low RLC AMre-transmission efficiency. Considering once again the first example,described above, assuming that MAC-hs segments the IP-packet into 38transport blocks. Hybrid Automatic Repeat Request (HARQ) is an advancedretransmission strategy, which allows the performing of possiblere-transmissions directly at the physical/MAC layer. This is donewithout involving higher-layer mechanisms and so reduces the delay.

Due to an error in the HARQ feedback signalling or an error caused bythe reaching of the maximum number of HARQ re-transmissions, all but oneof the respective transmission blocks may be successfully delivered. Insuch a case, the whole RLC PDU of a 1500 octet and an RLC header has tobe re-transmitted, resulting in a very low RLC re-transmissionefficiency.

Despite the obvious performance benefits gained from using a flexibleRLC according to the prior art, the scenario described above clearlyillustrates that there are situations when large RLC PDUs can createproblems, which typically occur at times of bad link quality, or whenthere are not enough of transmission resources in terms of power,spectrum or time-slots available.

SUMMARY

The object of the present invention is to address at least some of theproblems outlined above. More specifically, the present invention solvesthe aforementioned problems by providing and implementing an adaptivesegmentation limit according to the independent claims described below.

An adaptable segmentation limit, defining a threshold of a largestProtocol Data Unit (PDU) that is submitted to a lower protocol layer, isdeployed at a higher protocol layer interacting with the lower protocollayer. For each Service Data Unit (SDU) arriving at the higher protocollayer, it is determined if the respective SDU can fit into thesegmentation limit or not. Each SDU that do not fit into thesegmentation limit is segmented into PDUs which are smaller than orequal to the segmentation limit, while no segmentation is performed onSDUs that fit into the segmentation limit. The resulting PDU or PDUs arethen submitted to the lower protocol layer.

SDUs that remain after a segmentation or when no segmentation is foundnecessary may be concatenated if concatenation is supported.

The suggested adaptive segmentation may be executed using any of anumber of alternative conditions, either alone or in a combination. Oneor more PDUs may be set to the same size as the segmentation limit. PDUsmay match either the largest, or any transport block size that isavailable in the lower protocol layer. PDUs may also be set to equalsize if perfect division into PDUs of equal size is possible, or toapproximately equal size if perfect division is not possible.

The segmentation limit may be dynamically adapted on the basis of anindication, signalled from the lower protocol layer, including anotification, denoted the PDU size limit, of the largest PDU size whichis accepted by the lower protocol layer. The indication may be updatedand signalled to the higher protocol layer according to one or morealternative conditions. A change of the PDU size limit to a level, lowerthan a predefined updating threshold may define one way of triggeringsignalling of an indication. Unsuccessful delivering of PDUs from thelower protocol layer to a receiving peer may also trigger signalling ofan indication from the lower protocol layer to the higher protocollayer. The indication may also include a request for re-segmentation orto discard one or more SDUs.

The PDU size limit may be updated periodically or on the basis of one ormore monitored parameters, such as available or unblocked transportblocks, link quality, available scheduling grants or availableresources.

Alternatively, or in a combination, the segmentation limit may beadjusted on the basis of the residual loss-rate, observed in the higherprotocol layer. After having compared the observed loss-rate to aloss-rate threshold, the segmentation limit is adjusted by apredetermined amount. The observation may be executed periodically oraccording to any other predetermined condition.

Under favourable conditions, such as, e.g. high link quality, theproposed adaptive segmentation may be considered superfluous. Underthose circumstances the PDU limit may be set to a predetermined,relatively large size, which is signalled to the higher protocol layer.Since all SDUs will now fit into the segmentation limit, segmentationwill be cancelled until the segmentation limit is updated with a lowervalue.

A node is adapted to provide adaptive segmentation in a higher protocollayer interacting with a lower protocol layer which comprises: means fordeploying an adaptable segmentation limit the higher protocol layer,defining a threshold of the largest PDU to be submitted to a lowerprotocol layer; means for receiving one or more SDUs by the higherprotocol layer; means for determining for each SDU if the SDU can fitinto the segmentation limit or not; means for segmenting an SDU that donot fit into the segmentation limit, into PDUs which are smaller than orequal to the segmentation limit, or performing no segmentation on an SDUthat fit into the segmentation limit, and; means for submitting theresulting PDU/PDUs to the lower protocol layer. The segmenting means ofthe node may be adapted to perform concatenation according to thefollowing rules:

concatenating remaining SDUs into a PDU, which fit into the segmentationlimit, after having segmented one or more SDUs, or, in case nosegmentation is being performed; concatenating two or more SDUs into aPDU until the segmentation limit is reached.

Another node to be used in a communication network, providing adaptivesegmentation in a higher protocol layer interacting with a lowerprotocol layer of said node comprises the following means: means foradjusting a PDU size limit, defining the largest PDU size which isaccepted by the lower protocol layer; means for signalling anindication, including a notification of the PDU size limit to the higherprotocol layer, to be used when adaptively adjusting a segmentationlimit, defining a threshold of a largest PDU that is submitted to thelower protocol layer; means for receiving one or more PDUs, submittedfrom said higher protocol layer.

The higher protocol layer may be e.g. the RLC protocol layer, and theprotocol may be locate in a node such as e.g. an RNC, node B or a userequipment. The lower protocol layer may be e.g. the MAC protocol layer,which may be located in another node, e.g. a node B or a user equipment,interacting with the node comprising the higher protocol layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail by means ofexemplary embodiments and with reference to the accompanying drawings,in which:

FIG. 1 is a basic overview of a procedure, according to the prior art.

FIG. 2 a is an illustration of an evaluation situation where an SDU issmaller than a specified segmentation limit, in accordance with oneembodiment.

FIG. 2 b is an illustration of another situation in which an SDU islarger than a specified segmentation limit, in accordance with anotherembodiment.

FIG. 3 is a flow chart illustrating a basic procedure for deploying asegmentation limit in accordance with another embodiment.

FIG. 4 a is a flow chart illustrating a procedure for adaptivelyadjusting a segmentation limit in a higher protocol layer in accordancewith another embodiment.

FIG. 4 b is a flow chart illustrating an alternative procedure foradaptively adjusting a segmentation limit in an higher protocol layer inaccordance with yet another embodiment.

FIG. 5 a is a flow chart illustrating a procedure for adjusting a PDUsize limit in a lower protocol layer in accordance with anotherembodiment.

FIG. 5 b is a flow chart illustrating a procedure for adjusting a PDUsize limit in a lower protocol layer in accordance with yet anotherembodiment.

FIG. 6 is a schematic illustration of a node, having a higher protocollayer, responsible for performing adaptive segmentation and/orconcatenation, in accordance with another embodiment.

FIG. 7 is a schematic illustration of a node having a lower protocollayer, adapted to receive adaptively segmented and/or concatenated PDUsfrom a higher protocol layer, according to another embodiment.

DETAILED DESCRIPTION

Briefly described, the present invention provides a method and nodes ina communication network which are adapted for providing adaptivesegmentation and concatenation.

According to the claimed invention, adaptive segmentation and/orconcatenation is provided by way of introducing an adaptively adjustablesegmentation limit to be deployed in a higher protocol layer, which isresponsible for segmentation and/or concatenation. The higher protocollayer in question may be located in any type of node, adapted to performsegmentation and/or concatenation, such as, e.g. an RNC, a node B or auser equipment. The segmentation limit according to the claimedinvention defines a threshold of the largest PDU that is to be submittedto a lower protocol layer by a higher protocol layer sender, deployingsegmentation and/or concatenation. The lower protocol layer may belocated in, e.g. a node B, a user equipment or any other node to whichone or more PDUs are submitted from a higher protocol layer.

FIG. 2 a shows one possible scenario in which a segmentation limit 200has been deployed. The SDU 201 is found to fit into an approved PDUformat, i.e. the size of the resulting PDU does not exceed the largestacceptable PDU size, denoted the PDU size limit. When this condition ismet, a header will be attached to the SDU, and the resulting PDU 202,will be submitted from the protocol sender to a lower protocol layer,without performing any segmentation or concatenation in the higherprotocol layer. In the scenario described by FIG. 2 b, however, the sizeof the SDU 203 is found to be too large to fit into one PDU ofacceptable size, i.e. the SDU is larger than the segmentation limit 204.In this case, the SDU needs to be segmented, such that the sizes of eachresulting PDU 205 and 206 is less than or equal to the segmentationlimit. In the figure, the first PDU, PDU1, equals the size of thesegmentation limit, while the size of the second PDU, PDU 2 is smallerthan the segmentation limit.

One embodiment for using the proposed segmentation limit according toone embodiment will now be described with reference to FIG. 3.

FIG. 3 illustrates one way of providing adaptive segmentation and/orconcatenation by way of using a segmentation limit, starting at step300. At a next step 301, the adaptively adjustable segmentation limit isdeployed in a higher protocol layer responsible for performingsegmentation and/or concatenation. Initially the segmentation limit isset to a starting value, according to one or more predeterminedconditions. Alternative embodiments for adjusting the segmentation limitwill be described below with reference to FIGS. 4 a and 4 b.

Arriving SDUs, illustrated by step 302, to be submitted from a higherprotocol layer to a lower protocol layer as one or more PDUs, arecompared to the segmentation limit in a next step 303, where it isdetermined whether an SDU will fit into the segmentation limit or not.If the SDU is found not to fit into the segmentation limit, the SDU issegmented into PDUs which are smaller than or equal to the segmentationlimit in step 304, before the resulting PDUs are submitted to a lowerprotocol layer in step 305. If, however, an SDU is found to fit into thesegmentation limit, the resulting PDU is submitted without performingany segmentation. The described procedure is repeated for each arrivingSDU as long as the segmentation limit is deployed by the system. Ifsupported, the SDUs may be concatenated, either in combination withsegmentation or without using segmentation. SDUs which remain after asegmentation may be concatenated into a PDU, which fit into thesegmentation limit. If no segmentation is being performed, two or moreSDUs may be concatenated into a PDU until the segmentation limit isreached and no more SDU will fit into the PDU.

The segmentation which is performed in step 304 may be done according toone or more predefined rules, some of which will now be described.

According to a first embodiment, an SDU is segmented and/or concatenatedinto PDUs in such a way that the size of at least one PDU is equal tothe segmentation limit. In another embodiment, an SDU is segmentedand/or concatenated into equally sized PDUs which fit into thesegmentation limit. If, however, no division into equally sized PDUs ispossible, the respective SDU may instead be segmented and/orconcatenated into PDUs of approximately equal size. In yet anotherembodiment, an SDU may be segmented and/or concatenated into PDUs whichmatch any available transport block sizes in MAC, or, alternatively, thelargest available transport block.

In FIG. 4 a one embodiment for adjusting the segmentation limit isdescribed. The procedure, starting in step 400, is being executed in thehigher protocol layer which is responsible for segmentation and/orconcatenation. One way of providing adjustment of the segmentation limitis to indicate the largest PDU size to be accepted by a lower protocollayer, to which one or more PDUs are to be submitted. This indicationwill include a notification of the largest acceptable PDU size, herebydefined as the PDU size limit. The PDU size limit is adjusted in thelower protocol layer according to predetermined adjusting conditions andis also signalled to the higher protocol layer according topredetermined signalling conditions. In FIG. 4 a, a check for a newindication, comprising the proposed PDU size limit, is executed in step401. Such a checking procedure may be executed periodically or accordingto one or more alternative conditions. When an indication is received atthe higher protocol layer, the segmentation limit is adjusted, takingthe received PDU size limit into consideration. The adjustment, which isexecute in step 402, is done according to one or more predeterminedconditions.

An alternative way of adjusting the segmentation limit will now bedescribe with reference to FIG. 4 b. This alternative embodiment, whichstarts at step 403, refers to an updating procedure which is executed inthe higher protocol layer, responsible for segmentation andconcatenation. An observed residual loss-rate, which may be monitoredperiodically, is compared to an upper loss-rate threshold in step 404.If the loss-rate is found to be higher than the upper loss-ratethreshold, the segmentation limit is decreased with a pre-determinedamount in step 405.

In a next step 406 the loss rate is compared to a lower loss-ratethreshold. If the residual loss-rate is found to be below the lowerloss-rate threshold, the segmentation limit is instead increased with apre-determined amount in step 407. It is to be understood that the twoalternative embodiments described with reference to FIGS. 4 a and 4 bmay be implemented separately or in a combination.

One embodiment for adjusting a PDU size limit in a lower protocol layerand for signalling the PDU size limit to the respective higher protocollayer will now be described with reference to FIG. 5 a. The procedure,starting in step 500, may be executed periodically as long as asegmentation limit according to the claimed invention is deployed. Instep 501 it is determined if a predetermined condition for adjusting thePDU size limit has been triggered. Upon detecting that a condition foradjusting the PDU size limit has occurred, the PDU size limit isadjusted according to a predetermined rule. In a next step 503 it isdetermined if a predetermined condition for signalling the PDU sizelimit to a respective upper-layer protocol has occurred. If a signallingis triggered, the recently updated PDU size limit is signalled to therespective higher protocol layer in a final step 504, where theindication, comprising the PDU size limit will trigger an adjustingprocedure, adapted to adjust the segmentation limit, as described above.

The conditions for adjusting the PDU size limit may be defined accordingto different preferred criteria. According to one embodiment, aparameter, such as largest unblocked transport block, largest availabletransport block, link quality, available scheduling grants or availableresources may be monitored periodically, or according to any otherpredetermined rule. Available resources may comprise resources such astransmission power, frequency resources or time-slots. FIG. 5 billustrates a way of triggering an adjustment which has the purpose ofcancelling the segmentation limit when a quality parameter, which ismonitored in the lower protocol layer, indicates such a high qualitythat the use of a flexible segmentation is found superfluous. Such amonitoring is done in step 506 in the figure. In step 507, PDU sizelimit is set to a predefined, high value, hereby denoted maximum size.

By setting PDU size limit to maximum limit, the segmentation limit willbe adjusted to a value high enough to allow all possible SDUs to fitinto the segmentation limit. Since all SDUs will now fit into thesegmentation limit, segmentation practically will be cancelled until thesegmentation limit is updated with a lower value.

Also the conditions for triggering the signalling of the latest updatedPDU size limit may be set according to different preferences. Accordingto one embodiment, indications are configured to be signalled on aperiodical basis. In another embodiment an indication is configured tobe signalled when PDU size limit is found to be lower than a pre-definedupdating threshold. In yet another embodiment an indication is insteadsignalled when it is found that PDU size limit has been changed above acertain configurable amount, in order to reduce the amount of indicationmessages, sent from the lower protocol layer to the respective higherprotocol layer. The proposed alternative adjustment trigger conditions,as well as the alternative signalling trigger conditions mentionedabove, may be implemented alone or in any alternative combination.

The proposed indication may be used also for forwarding additionalinstructions in connection with the proposed adjusting procedure.According to one embodiment, the indication also includes a request forre-segmentation from the respective higher protocol layer. Such arequest may comprise an explicit indication of all PDUs to bere-segmented. Alternatively, a request may comprise the lastsuccessfully transmitted PDU. Such a request may result in that allsubsequent PDUs are re-segmented by the respective higher protocollayer. In yet another embodiment the indication may comprise a requestto the respective higher protocol layer to discard a number of SDUs,when it is found that the lower protocol layer has failed to transmitthe respective SDUs, due to excessive size. Another condition forrequesting for discarding of SDUs may be if it has been estimated that anumber of SDUs can not be successfully transmitted within apredetermined time-limit.

The functionality in a node suitable for performing segmentation and/orconcatenation according to one embodiment will now be schematicallydescribed with reference to FIG. 6. It is to be noted that this node 600could be any type of communication node which is adapted to performsegmentation and/or concatenation. An SDU received in a receiving means601 is forwarded to a determining means 602 for determining whethersegmentation and/or concatenation is to be executed. The determiningmeans comprises means for deploying a segmentation limit according toany of the embodiments proposed above, and means for determining if areceived SDU fit into the segmentation limit or not. Next, the SDU ispassed to a segmentation and concatenation means 603, where the SDU issegmented and/or concatenated according to any of the embodimentsproposed above if the SDU if found not to fit into the segmentationlimit by the determining means. The resulting PDUs are then submitted toa respective lower protocol layer by a submitting means 604. If,however, the SDU if found to fit into the segmentation limit, theresulting on or more PDUs are submitted to a respective lower protocollayer by the submitting means according to conventional procedures.

According to the different proposed embodiments of the claimedinvention, a PDU size limit is updated and signalled in a lower protocollayer, adapted to receive PDUs, submitted from a higher protocol layer.FIG. 7 schematically illustrates the functionality necessary forproviding such a service to the higher protocol layer. The node 700comprises an adjusting means adapted to adjust a PDU size limit when anadjustment trigger has been activated. The latest updated PDU size limitis signalled to the respective higher protocol layer from a signallingmeans 702 when a signalling trigger has been activated. The signallingmeans also may comprise means adapted to determine which PDUs that havebeen successfully transmitted, and means adapted to include a request todiscard a number of SDUs, when it has been determined that transmittingof these SDUs has failed due to excessive size.

This means also may be adapted to use an estimating scheme forestimating whether a number of SDUs can be transmitted successfullywithin a predetermined time-limit or not. Also the result from thisestimation may be used for requesting for a number of SDUs to bediscarded in the higher protocol layer.

While the invention has been described with reference to specificexemplary embodiments, the description is generally only intended toillustrate the inventive concept and should not be taken as limiting thescope of the invention, which is defined by the appended claims.

What is claimed is:
 1. A method of providing adaptive segmentation in ahigher protocol layer interacting with a lower protocol layer,comprising: deploying an adaptable segmentation limit at the higherprotocol layer which defines a threshold of a largest Protocol Data Unit(PDU) to be submitted to the lower protocol layer; determining, at thehigher protocol layer and for each arriving Service Data Unit (SDU),whether the SDU can fit into the segmentation limit; segmenting, at thehigher protocol layer, each SDU that does not fit into the segmentationlimit into PDUs which are smaller than or equal to the segmentationlimit, and performing no segmentation on each SDU that fits into thesegmentation limit, such that arbitrary PDU sizes are used that aresmaller than or equal to the segmentation limit; and submitting theresulting one or more PDUs to the lower protocol layer.
 2. The method ofclaim 1 wherein the segmenting further comprises: concatenatingremaining SDUs into a PDU which fits into the segmentation limit, afterhaving segmented one or more SDUs; or if no segmentation is beingperformed, concatenating two or more SDUs into a PDU until thesegmentation limit is reached.
 3. The method of claim 1 wherein thedeploying comprises dynamically adapting the segmentation limit based onan indication signaled from the lower protocol layer.
 4. The method ofclaim 3 wherein the indication includes a notification of a PDU sizelimit defining the largest PDU size which is accepted by the lowerprotocol layer.
 5. The method of claim 1 wherein the segmentation limitis adjusted based on an observation of residual loss rate in the higherprotocol layer.
 6. The method of claim 5 wherein the residual loss rateis monitored periodically in the higher protocol layer.
 7. The method ofclaim 5: wherein, upon observing that the residual loss rate is above apredetermined loss rate threshold, the segmentation limit is adjusted bylowering the segmentation limit by a predetermined decreasing amount;and wherein, upon observing that the residual loss rate is below theloss rate threshold, the segmentation limit is adjusted by increasingthe segmentation limit by a predetermined increasing amount.
 8. Themethod of claim 1 wherein the segmenting comprises segmenting each SDUto be segmented into one of the following: at least one PDU of the samesize as the segmentation limit; PDUs that match a transport block sizethat is available in the lower protocol layer; PDUs that match thelargest transport block size that is available in the lower protocollayer; PDUs of equal size if perfect division into PDUs of equal size ispossible; and PDUs of approximately equal sizes if perfect division intoPDUs of equal size is not possible.
 9. The method of claim 1 wherein thehigher protocol layer is a Radio Link Control (RLC) protocol layer. 10.The method of claim 1 wherein the higher protocol layer is located in aRadio Network Controller (RNC) or in a user equipment.
 11. The method ofclaim 1 wherein the lower protocol layer is a Medium Access Control(MAC) protocol layer.
 12. The method of claim 1 wherein the lowerprotocol layer is located in any of a Node B, a Radio Network Controller(RNC), or a user equipment.
 13. The method of claim 1 wherein the higherprotocol layer and the lower protocol layer are located in differentnodes.
 14. A method of adaptively adjusting a segmentation limit, themethod being implemented by a node in a communication network andcomprising: defining a threshold of a largest Protocol Data Unit (PDU)that is to be submitted from a higher protocol layer to a lower protocollayer interacting with the higher protocol layer, the threshold beingused for deploying adaptive segmentation, such that arbitrary PDU sizesare used that are smaller than or equal to the threshold; wherein thesegmentation limit is dynamically adapted based on an indicationsignaled from the lower protocol layer to the higher protocol layer. 15.The method of claim 14 wherein the indication includes a notification ofa PDU size limit, defining a largest PDU size which is accepted by thelower protocol layer.
 16. The method of claim 15 wherein the indicationis signaled to the higher protocol layer periodically.
 17. The method ofclaim 16 wherein the indication further includes a request to the higherprotocol layer to discard a number of SDUs when: the lower protocollayer has failed to transmit the SDUs due to excessive SDU size; or ithas been estimated by the lower layer protocol that the SDUs cannot betransmitted successfully within a predetermined time limit.
 18. Themethod of claim 15 wherein the indication is signaled to the higherprotocol layer when it is found that the PDU size limit has been changedto a level lower than a predefined updating threshold.
 19. The method ofclaim 15 wherein the indication is signaled to the higher protocol layerwhen the PDU size limit has been changed by a configurable amount. 20.The method of claim 15 wherein the indication is signaled to the higherprotocol layer when the lower protocol layer receives an SDU from thehigher protocol layer which was too large to be successfully deliveredto a receiving peer by the lower protocol layer.
 21. The method of claim15 wherein the indication further includes a request to the higherprotocol layer to re-segment a number of SDUs into a smaller PDU sizewhere: each PDU that is required to be re-segmented by the higherprotocol layer is explicitly indicated; or a reference indicating whichsequence number and forward re-segmentation is required.
 22. The methodof claim 15 wherein the PDU size limit is updated in the lower protocollayer based on at least one of the following parameters: a largestunblocked transport block; a largest available transport block; a linkquality; available scheduling grants; and available resources.
 23. Themethod of claim 22 wherein the available resources comprise any of thefollowing resources: transmission power; frequency resources; and timeslots.
 24. The method of claim 22 wherein the at least one parameter ismonitored periodically in the lower protocol layer.
 25. The method ofclaim 24 wherein upon observing that the value of the parameter is abovea predetermined quality threshold, the PDU size limit is set to apredetermined, maximum size.
 26. The method of claim 25 wherein the PDUsize limit is signaled to the higher protocol layer when it has beenset.
 27. A node in a communication network, the node being operative toprovide adaptive segmentation in a higher protocol layer interactingwith a lower protocol layer, the node comprising one or more processingcircuits configured to: deploy an adaptable segmentation limit at thehigher protocol layer that defines a threshold of a largest PDU to besubmitted to a lower protocol layer; receive one or more SDUs in thehigher protocol layer; determine, for each SDU, whether the SDU can fitinto the segmentation limit; segment an SDU that does not fit into thesegmentation limit into PDUs which are smaller than or equal to thesegmentation limit, and perform no segmentation on an SDU that fits intothe segmentation limit, such that arbitrary PDU sizes are used that aresmaller than or equal to the segmentation limit; and submit theresulting one or more PDUs to the lower protocol layer.
 28. The node ofclaim 27 wherein the one or more processing circuits are configured tosegment the SDU by being configured to: concatenate remaining SDUs intoa PDU, which fits into the segmentation limit, after having segmentedone or more SDUs; or if no segmentation is being performed, concatenatetwo or more SDUs into a PDU until the segmentation limit is reached. 29.The node of claim 27 wherein the one or more processing circuits arefurther configured to change the segmentation limit with a configurableamount based on an indication signaled from the lower protocol layer.30. The node of claim 29 wherein the indication includes a notificationof a PDU size limit, defining the largest PDU size which is accepted bythe lower protocol layer.
 31. The node of claim 27 wherein the one ormore processing circuits are configured to segment an SDU into one ofthe following: at least one PDU of the same size as the segmentationlimit; PDUs that match a transport block size that is available in thelower protocol layer; PDUs that match a largest transport block sizethat is available in the lower protocol layer; PDUs of equal size ifperfect division into PDUs of equal size is possible; or PDUs ofapproximately equal sizes if perfect division into PDUs of equal size isnot possible.
 32. The node of claim 27 wherein the one or moreprocessing circuits are further configured to adaptively adjust thesegmentation limit based on an observation of residual loss rate in thehigher protocol layer.
 33. The node of claim 32 wherein the one or moreprocessing circuits are further configured to monitor the residual lossrate periodically.
 34. The node of claim 32 wherein the one or moreprocessing circuits are configured to adjust the segmentation limit bybeing configured to: lower the segmentation limit by a predetermineddecreasing amount if the residual loss rate is found to be above apredetermined loss rate threshold; and increase the segmentation limitby a predetermined increasing amount if the residual loss rate is foundto be below the loss rate threshold.
 35. The node of claim 27 whereinthe higher protocol layer is a Radio Link Control (RLC) protocol layer.36. The node of claim 27 wherein the node is any of a Radio NetworkController (RNC), a Node B or a user equipment.
 37. The node of claim 27wherein the lower protocol layer is a Medium Access Control (MAC)protocol layer.
 38. A node in a communication network operative toprovide adaptive segmentation in a higher protocol layer interactingwith a lower protocol layer of the node, the node comprising one or moreprocessing circuits configured to: adjust a PDU size limit defining thelargest PDU size which is accepted by the lower protocol layer; signalan indication including a notification of the PDU size limit to thehigher protocol layer, to be used when adaptively adjusting asegmentation limit, such that arbitrary PDU sizes are used that aresmaller than or equal to the segmentation limit; receive one or morePDUs submitted from the higher protocol layer.
 39. The node of claim 38wherein the one or more processing circuits are configured to update thePDU size limit periodically.
 40. The node of claim 38 wherein the one ormore processing circuits are configured to signal the indicationperiodically.
 41. The node of claim 38 wherein the one or moreprocessing circuits are configured to signal the indication when the PDUsize limit is changed by a configurable amount, in order to reduce theamount of indication messages.
 42. The node of claim 38 wherein the oneor more processing circuits are configured to signal the indication whenthe lower protocol layer has received an SDU from the higher protocollayer which was too large to be successfully delivered to a receivingpeer by the lower protocol layer.
 43. The node of claim 39 wherein theone or more processing circuits are configured to determine which PDUshave been transmitted successfully, and include a request in theindication to the higher protocol layer to discard a number of SDUswhen: it has been determined that the lower protocol layer has failed totransmit the SDUs due to excessive SDU size; or it has been estimatedthat the SDUs cannot be transmitted successfully within a predeterminedtime limit.
 44. The node of claim 39 wherein the one or more processingcircuits are configured to update the PDU size limit based on at leastone of the following parameters: a largest unblocked transport block; alargest available transport block; a link quality; available schedulinggrants; and available resources.
 45. The node of claim 44 wherein theavailable resources comprise any of the following resources:transmission power; frequency resources; and time slots.
 46. The node ofclaim 44 wherein the one or more processing circuits are configured tomonitor the at least one parameter periodically.
 47. The node of claim44 wherein the one or more processing circuits are configured to set thePDU size limit to a predetermined, maximum size if it is determined thatthe parameter is above a predetermined quality threshold.
 48. The nodeof claim 47 wherein the one or more processing circuits are configuredto signal the PDU size limit to the higher protocol layer when it hasbeen updated.
 49. The node of claim 38 wherein the node is a Node B or auser equipment.
 50. The node of claim 38 wherein the higher protocollayer is the Radio Link Control (RLC) protocol layer.
 51. The node ofclaim 38 wherein the lower protocol layer is the Medium Access Control(MAC) protocol layer.